Non-opioid Anti-nociceptive Effect of Psidium guajava Leaves Extract

Objective: The main aim was to demonstrate the anti-nociceptive effects of Psidium guajava leaves extract. Methods: Ethanol extract of P. guajava leaves was administered intraperitoneally to mice 30 min before administration of acetic acid. The number of abdominal constriction was noted. Results: P. guajava leaves extract showed statistically significant decrease in abdominal constriction (writhing) when compared to controls. The percentage inhibition was 20.9, 53.9 and 97.3 for 2, 3 and 4 mg/kg extract respectively. These mice showed normal behavior and motor activity. The antinociceptive effect was statistically similar to equivalent doses of mefenamic acid. Morphine, an opioid analgesic revealed 29.0, 57.3 and 100.0 inhibition of abdominal constriction for 0.2, 0.3 and 0.4 mg/kg respectively. Interestingly, pretreatment with Naloxone did not significantly decrease the analgesic effect of P. guajava leaves extract. Conclusions: Results from this present study revealed P. guajava extract exerted a potent anti-nociceptive effect, which was similar potency to mefenamic acid and 10 times less potent to morphine. The antinociceptive effects were dose-dependent, without behavior changes and may not involve the opioid receptors.